This invention relates to a carburetor, and more particularly to a rotary throttle valve carburetor for a two cycle engine.
A fuel and air mixture is fed into a crankcase of an operating two cycle engine from a conventional rotary throttle valve carburetor via negative pressure. Within the carburetor, fuel flows from a fuel metering chamber into an air intake channel. Within the channel, the fuel mixes with air and is then drawn into the crankcase. From the crankcase, the fuel and air mixture flows into a combustion chamber and is burned. Relative to other combustion engines, the combustion process of conventional two cycle engines is inefficient. The fuel to air mixture does not completely burn and the resultant air pollutants from the exhaust are relatively high. To alleviate some of the air pollutant concerns, the industry is trending toward a leaner fuel to air mixture to achieve a cleaner burn. The dynamics or isolated transients of the mixing and burning process during acceleration and deceleration of the two cycle engine offer a variety of design challenges.
One such transient occurs during deceleration of the two cycle engine when negative pressure within the air intake channel of the rotary throttle valve carburetor increases causing excessive fuel to be drawn through a fuel feed tube and mix with air within the intake channel. When this occurs, the subsequent fuel and air mixture is too rich and the combustion process is not capable of burning all the fuel. The exhaust is therefore affected and the air pollutants rise.
Because the fuel in the fuel metering chamber is directly drawn into the throttling bore of the rotary throttle from a fuel jet orifice through the fuel feed tube, the mixing of fuel and air, i.e. vaporization, is incomplete. Accordingly, it is difficult to attain lean-mixture combustion in the combustion chamber of a two cycle engine.
A rotary throttle valve carburetor for a two cycle engine has a rotary throttle disposed transversely through an air intake channel through a carburetor body. The rotary throttle rotates and moves vertically within a cylindrical chamber defined by the carburetor body. A throttling bore laterally extends through the rotary throttle and adjustably aligns longitudinally with the air intake channel. The rotary throttle supports a needle extending therefrom longitudinally into a fuel feed tube supported at one end by the carburetor body. The fuel feed tube provides a path for fuel flow from a fuel metering chamber.
An air passage defined by the carburetor body communicates between an intake portion of the air intake channel and a passageway which communicates with the throttling bore of the rotary throttle. The passageway is formed between an air guide tube and the fuel feed tube. Preferably, the rotary throttle supports the air guide tube which is concentric to the fuel feed tube. A bottom space communicates between the air passage and the passageway. An annular face of the carburetor body penetrated by the fuel feed tube and an under annular face of the rotary throttle axially define the bottom space. The air passage communicates with the bottom space through the annular face of the carburetor body. A fuel jet orifice extends laterally through the fuel feed tube thereby emitting fuel transversely into the passageway.
Objects, features and advantages of this invention include reducing air intake vacuum during deceleration transients of the two cycle engine to prevent excessive fuel draw, avoiding overly rich fuel to air mixture, increasing vaporization of the fuel within the throttling bore, and decreasing engine exhaust emissions.